Fabrication of a scintillator material of elpasolite type

ABSTRACT

A process for fabricating a crystalline scintillator material with an elpasolite structure that has a theoretical composition of A 2 BC (1-y) M y X (6-y)  can include conducting crystallization by cooling from a melt bath including r moles of A and s moles of B. A is chosen from Cs, Rb, K, and Na. B is chosen from Li, K, and Na. C is chosen from athe rare earth elements, Al, and Ga. M is chosen from the alkaline earth elements. X is chosen from F, Cl, Br, and I, and y represents the atomic fraction of substitution of C by M and is in the range extending from 0 to 0.05. The melt bath can be in contact with the material containing A and B in such a way that 2s/r is above 1. The process shows an improved fabrication yield. The crystals formed therefrom can have improved scintillation properties.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation-in-part of and claims priorityunder 35 U.S.C. §120 to International Application No. PCT/FR2014/050893,filed Apr. 11, 2014, which claims priority to French Patent ApplicationNo. 1353354, filed Apr. 12, 2013, both of which applications areincorporated by reference herein in their entireties.

FIELD OF THE DISCLOSURE

This disclosure generally relates to a crystalline material including anelpasolite phase and a process for fabricating a crystalline materialincluding an elpasolite phase. Particularly, this disclosure relates toa monocrystalline material including a rare earth or metal halideelpasolite phase and a process of forming.

DESCRIPTION OF RELATED ART

Scintillator materials are widely used for detecting gamma or X-rays aswell as energetic particles such as alpha particles, neutrons etc.

Scintillation relies on the physical principle of the conversion of theenergy of photons, incident X or gamma radiation or energetic particlesinto light in or near the visible spectrum. Notably, inorganicscintillators are preferably monocrystalline or polycrystalline. Asingle crystal allows easier extraction of light thanks to the absenceof internal diffusion across grain boundaries, heterogeneities and otherdefects present in polycrystalline materials. A state of goodcrystallinity is necessary, as it determines the most effectivescintillation mechanisms. The extracted light is then collected by adevice well known to those skilled in the art as a photomultiplier tube,a photodiode, a SiPM (silicon photomultiplier), an APD (avalanchephotodiode) etc. A polycrystalline scintillator can be produced frompowders that are compacted, sintered or coated with a binding agent soas to allow extraction of light. Often, these non-monocrystallinematerials are too opaque beyond a certain thickness, a thickness that ismoreover insufficient to stop enough incident energetic particles orphotons. Generally, a monocrystalline scintillator material ispreferred. The detection of gamma photons, alpha or beta particles,charged particles or neutrons is of major benefit in many applicationsin nuclear medicine, fundamental physics, for baggage security scanners(detection portals), the continuous monitoring of containers and trucksat borders, geophysical diagnostic systems in mines and for oildrilling, etc. In these applications, it is moreover often desirable tobe able to tell neutrons apart from gamma radiation and a scintillationdetector should in this case be able to produce signals of differentluminescence characteristics depending on the type of radiation.

The conventional procedure of those skilled in the art seeking tofabricate an elpasolite single crystal is to carry out a crystallizationbased on a melt bath, the composition of which corresponds to thestoichiometry of the crystal in question. Whatever the process ofcrystalline growth used, for a large number of complex compositions(three-component or even more complex) the phenomenon of incongruentfusion exists. The crystallization of a main phase of elpasolite isaccompanied or preceded by the precipitation of a secondary phase thatcan appear in the form of inclusions or of a single-phase region of anundesirable phase. It has now been noticed that the crystalline materialobtained from the melt bath of these complex compositions contains ahigh proportion of inclusions, or is even solely composed of thesecondary unwanted phase. The crystalline material obtained, of thesingle-crystal or polycrystal type, can also be called the ingot. In thecase of a single crystal made from incongruent fusion, the secondaryphase is generally located at the ends or around the perimeter of themonocrystalline material. This secondary phase forms non-transparentregions disturbing the monocrystalline nature of the main phase. Incertain favorable cases, it is nonetheless possible to recover part ofthe monocrystalline material while subsequently eliminating theseunusable regions by cutting out and preserving the transparentmonocrystalline part that is free of inclusions. These inclusionscorrespond to unwanted phases of a different composition to that sought.According to this disclosure, a means has been discovered for reducingthe proportion of these impure regions, or even in certain cases ofeliminating them, and providing better fabrication yields in doing so.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments are illustrated by way of example and are not limited by theaccompanying figures.

FIGS. 1a to 1c . represent ingots taken out of their phial aftercrystalline growth of Bridgman type.

FIGS. 2a to 2c represent ingots after crystalline growth of Czochralskitype.

Skilled artisans appreciate that elements in the figures are illustratedfor simplicity and clarity and have not necessarily been drawn to scale.For example, the dimensions of some of the elements in the figures canbe exaggerated relative to other elements to help improve understandingof embodiments of the invention. The use of the same reference symbolsin different drawings indicates similar or identical items.

DETAILED DESCRIPTION

The following description in combination with the figures is provided toassist in understanding the teachings disclosed herein. The followingdiscussion will focus on specific implementations and embodiments of theteachings. This focus is provided to assist in describing the teachingsand should not be interpreted as a limitation on the scope orapplicability of the teachings.

As used herein, the terms “comprises,” “comprising,” “includes,”“including,” “has,” “having,” or any other variation thereof, areintended to cover a non-exclusive inclusion. For example, a process,method, article, or apparatus that comprises a list of features is notnecessarily limited only to those features but can include otherfeatures not expressly listed or inherent to such process, method,article, or apparatus. Further, unless expressly stated to the contrary,“or” refers to an inclusive-or and not to an exclusive-or. For example,a condition A or B is satisfied by any one of the following: A is true(or present) and B is false (or not present), A is false (or notpresent) and B is true (or present), and both A and B are true (orpresent).

The use of “a” or “an” is employed to describe elements and componentsdescribed herein. This is done merely for convenience and to give ageneral sense of the scope of the invention. This description should beread to include one or at least one and the singular also includes theplural, or vice versa, unless it is clear that it is meant otherwise.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this disclosure belongs. The materials, methods, andexamples are illustrative only and not intended to be limiting. To theextent not described herein, many details regarding specific materialsand processing acts are conventional and can be found in textbooks andother sources within the scintillation and radiation detection arts.

This disclosure provides means for reducing the proportion of impureregions or a secondary phase included in a crystalline material duringits growth. In particular cases, formation of impure regions or asecondary phase can be prevented.

In addition to obtaining better fabrication yields, the presentdisclosure makes it possible to obtain crystals of the compositioncloser to the theoretical stoichiometry of elpasolite, or even to enrichit in certain cases, notably with certain elements such as Li. Enrichingwith Li is advantageous for neutron detection. In most cases, acomposition closer to the theoretical stoichiometry translates into abetter transmission of light and, in scintillation, by a better energyresolution. Moreover, the present disclosure allows the use of theso-called Czochralski growth process, which has until now beenconsidered by those skilled in the art as being impossible forincongruent fusion crystals and in particular the majority of crystalsof the elpasolite family. In Bridgman growth, the process according tothis disclosure makes it possible to obtain higher material yields ofusable crystal, i.e. it leads to an ingot comprising less unwanted phasefor an incongruent fusion elpasolite.

This disclosure relates to a process for fabricating a crystallinescintillator material and the crystalline scintillator material itself.In particular, this disclosure relates to a process for fabricating acrystalline scintillator material with a structure of elpasolite type oftheoretical compositionA₂BC_((1-y))M_(y)X_((6-y))  (1)

-   -   wherein    -   A is chosen from among Cs, Rb, K, Na,    -   B is chosen from among Li, K, Na,    -   C is chosen from among the rare earths, Al, Ga,    -   M is chosen from among the alkaline earths, particularly Ca, Mg,        Sr, Ba    -   X is chosen from among F, Cl, Br, I,        y representing the atomic fraction (or molar fraction) of        substitution of C by M (the elements C and M occupy the same        sites of the elpasolite) and being in the range extending from 0        to 0.05 (which means that y can be zero), comprising its        crystallization by cooling from a melt bath comprising r moles        of A and s moles of B, the melt bath in contact with the        material containing A and B in such a way that 2s/r is above 1.

The above remark does not mean that the crystalline scintillatormaterial actually obtained by the process according to the invention hasthe theoretical stoichiometric composition. It means that it leads to acrystal, the formula of which would be the formula (1) if itscomposition was actually theoretical (i.e. stoichiometric).

The formulae of materials actually produced can be determined fromelementary analyses (ICP—inductively coupled plasma—or XRF—X-rayfluorescence) of each element (except Li in the case of XRF) and withthe convention that the sum of the cations is 4 in the formula of theelpasolite.

The fact that the ratio 2s/r is above 1 is representative of an “excessof B” in the melt bath in the context of the present disclosure. It isin this sense that the expression “excess of B” can be used in thecontext of the present application. Indeed, the stoichiometrictheoretical elpasolite is such that the ratio of the double of thenumber of moles of B to the number of moles of A is equal to 1. It hasnow been found that this ratio in the crystal actually produced was inreality below 1, working with a 2s/r of 1, and that it is by increasingthe 2s/r ratio related to the melt bath that it is possible to approachand even to reach, or even exceed, the stoichiometric atomic (or molar)ratio of B to A in the elpasolite actually produced.

Preferably, 2s/r is above 1.05 and more preferably still above 1.25 andeven above 1.5. In particular, 2s/r can be above 1.15. Moreparticularly, 2s/r can be above 1.35. In the case of an excessivelylarge excess of B (excessively high 2s/r ratio), an unwanted phase canform, also giving rise to harmful inclusions. Preferably, the molarexcess of B in the bath (and therefore the 2s/r ratio) is insufficientto generate the formation of a phase of B₃C_((1-y))M_(y)X₆ at the startof crystallization, and at the very least it is low enough to generatesaid formation as little as possible. Thus, 2s/r is preferably below 10and more preferably still below 5. In particular, 2s/r can be below 3.

The 2s/r ratio is calculated from the molar quantities of A and Bintroduced into the bath. The elements A and B are introduced to it inhalogenated form. For the case in which the bath contains K or Na, giventhat these elements can go to A-type sites or to B-type sites, it isadvisable to determine the proportion of these elements going to the Asites and the B sites by experiment, in order to then be able tocalculate the 2s/r ratio. To determine the proportion of Na and K foundon one or the other site, a structural study can be carried out usingX-ray diffraction. To do this, a sealed sample holder is used,preventing the powder from hydrating in contact with the ambient air andtherefore becoming damaged. Indeed, these materials are very stronglyhygroscopic. According to this disclosure, the excess of Na or K asB-type element is therefore determined a posteriori from the exactformula of the elpasolite finally produced by determining the relativepercentage of Na or K on the A-type site or the B-type site. In general,the Na will predominantly go to the B-type site. By way of example, if acrystallization has been conducted from a bath containing 1.7 moles ofCsCl, 1.5 moles of LiCl, 0.5 moles of NaCl and 2 moles of YCl₃, and thatthe Na contained in the elpasolite actually crystallized is at 80% onthe B-type sites and at 20% on the A sites, then the 0.5 moles of Na canbe virtually broken down in the bath into 0.1 moles of NaCl of ACI typeand 0.4 moles of NaCl of BCI type. The bath therefore contains 1.8 molesof ACI (1.7 moles of CsCl+0.1 moles of NaCl), 1.9 moles of BCI (1.5moles of LiCl+0.4 moles of NaCl) and 2 moles of Ycl₃. The 2s/r ratio istherefore of 2.1.

The components carrying A, B, C and M are present in the melt bath inthe form of halide, the halogen of which corresponds to the X of theformula (1). Several different X halogens can be present in the meltbath if the final crystal must contain different X halogens. If trepresents the number of moles of C in the melt bath, and if urepresents the number of moles of M in the melt bath, then preferably,the ratio 2(t+u)/r is in the range extending from 0.8 to 1.2.Preferably, u/(t+u) is below 0.1. In particular, u can be zero.

The crystalline elpasolite obtained by the process according to thisdisclosure can have a real formula that is very close to theoreticalstoichiometry. This real formula can be represented by the formulaA_(a)B_(b)C_(c)M_(m)X_(x)  (2)in which A, B, C, M and X have the significance given previously, and a,b, c, m and x represent the respective atomic fractions of the A, B, C,M and X atoms. The atomic ratio 2b/a is in the range extending from 0.97to 1.4 (the limits are therefore included in the range), this 2b/a ratiobeing generally below 1.2.

The crystal according to this disclosure is in the majority of cases offace-centered cubic elpasolite crystalline structure of space group “Fm3 m”. With the convention that the sum of the atomic fractions of thecations (i.e. a+b+c+m) is equal to 4, generally, a is in the rangeextending from 1.7 to 2.3, b is in the range extending from 0.8 to 1.2,c is in the range extending from 0.85 to 1.1, m is in the rangeextending from 0 to 0.05 and x is in the range extending from 5.05 to6.9.

In the process according to this disclosure, the excess of B ispreferably enough for the ratio of the double of the atomic fraction ofthe B-type element to the atomic fraction of the A-type element(therefore the 2b/a ratio in formula (2)) in the elpasolite actuallyproduced to be of at least 0.97.

In the formulae (1) and (2), A can be a mixture of several elementschosen from among Cs, Rb, K and Na. Similarly, B can be a mixture ofseveral elements chosen from among Li, K or Na. This disclosure moreparticularly relates to cases where B comprises Li. More particularly, Bis simply Li. Similarly, C can be a mixture of several elements chosenfrom among the rare earths (which includes Sc and Y), Al and Ga.Similarly, M can be a mixture of several elements chosen from among thealkaline earths, particularly a mixture of several elements chosen fromamong Ca, Mg, Sr or Ba. Equally, X can be a mixture of several elementschosen from among F, Cl, Br and I. In particular, X comprises Cl, Br andI.

In particular cases, A comprises Cs, B comprises Li and X comprises Clor Br. In a more particular case, A comprises Cs, B comprises Li, Ccomprises La and X comprises Br. In another more particular case, Acomprises Cs, B comprises Li, C comprises Y and X comprises Cl.

The rare earth is an element of the Lanthanides from La to Lu, or Sc orY (these last two elements are similar to rare earths). In particularcases, C comprises a rare earth chosen from among the Lanthanides fromLa to Lu, or Y. The elpasolite is doped by an activating elementconferring or improving its scintillation behavior. The activatingelement is at least a rare earth chosen from among Ce, Pr, Eu, Tb andNd. It can be a mixture of activators, notably Ce and Pr. The activatingelement is part of the elements of C type. In general, the activator C″is present with a lower atomic fraction c″ in the elpasolite thananother element C′ also of C type, notably Y, said element C′ beingpresent with the atomic fraction c′. If C represents a mixture of twoelements C′ and C″ (notably Y and Ce respectively), then the atomicfraction c of the C-type element is such that c=c′+c″. The atomicfraction c″ of the activating element C″ is such that c″/(c+m) is above0.00001 and below or equal to 0.1, c representing the atomic fraction ofelement C (which includes all the C-type elements, therefore the elementC′) and m being the atomic fraction of element M. The elements C and Moccupy the same sites in the crystal lattice of the elpasolite. Theelpasolite can also contain a mixture of activators, notably Ce and Pr.In this case, the elpasolite contains three C-type elements (all onC-type sites), C′, C″ and C′″ (for example specifically Y, Ce and Prrespectively), the latter element being present with the atomic fractionc′″. In this case, (c″+c′″)/(c+m) is above 0.00001 and below or equal to0.1. The presence of M in the elpasolite, notably Sr, modifies theviscosity, the melting temperature of the mixture to be melted, theinfra-red emissivity of the melt bath and the surface tension of themelt bath. The presence of M in the crystal, particularly Sr, can modifyits scintillation properties such as its light output and its energyresolution.

This disclosure more particularly relates to scintillator materials offormulae (1) and (2) above for which B comprises Li, X comprises Cl, Bror I, and C comprises a rare earth chosen from among the Lanthanidesfrom La to Lu, or Y, the scintillator material being doped with anelement that will activate its scintillation. The materials of formulae(1) and (2) above can notably be such that B is Li, X is chosen fromamong Cl, Br or I, and C is chosen from among the Lanthanides from La toLu, or Y, the scintillator material being doped with an element thatwill activate its scintillation. Notably, the material according to thepresent disclosure may not comprise fluoride. Scintillator materialsproduced according to the present disclosure can have a high lightoutput, particularly measured with a gamma excitation of 662 keV.Notably, the light output can be above 15000 photons/MeV. A materialrich in LaBr₃, such as CLLB, can have a light output above 25000photons/MeV.

Scintillator materials produced according to this disclosure can have anexcellent energy resolution (small full width at half-maximum of thescintillation peak). Scintillation measurements can be performed with asource of gamma rays of ¹³⁷Cs type, a photomultiplier, and a standardmeasurement subsystem. Scintillator materials produced according to thepresent disclosure can have an energy resolution below 6%, or even below5%, values measured with a source of ¹³⁷Cs gamma rays. This disclosuremore particularly relates to cases where in the formulae (1) and (2) Bcomprises Li. This disclosure more particularly relates to cases wherein the formulae (1) and (2) A comprises Cs, and B comprises Li. Thisdisclosure more particularly relates to cases where in the formulae (1)and (2) A comprises Cs, B comprises Li and C comprises La. Thisdisclosure more particularly relates to cases where in the formulae (1)and (2) A comprises Cs, B comprises Li, C comprises La and X comprisesBr, and particularly when X is at over 80% in moles Br (80% in moles ofX is Br).

This disclosure more particularly relates to cases where in the formulae(1) and (2) A comprises Cs, B comprises Li and C comprises Y. Thisdisclosure more particularly relates to cases where in the formulae (1)and (2) A comprises Cs, B comprises Li, C comprises Y and X comprisesCl, particularly when X is at over 80% in moles Cl (80% in moles of X isCl).

The elpasolite can notably be of theoretical composition:

-   -   doped or undoped Cs₂LiYCl₆ and particularly Cs₂LiYCl₆:Ce, a        component usually called “CLYC” by those skilled in the art;    -   doped or undoped Cs₂LiLaBr₆, and particularly Cs₂LiLaBr₆:Ce, a        component usually called “CLLB” by those skilled in the art;    -   doped or undoped Cs₂LiLaBr_(6(1-z))Cl_(6z) with z ranging from 0        to 1, and particularly Cs₂LiLaBr_(6(1-z))Cl_(6z):Ce;    -   doped or undoped Cs₂LiLaCl₆ and particularly Cs₂LiLaCl₆:Ce a        component usually called “CLLC” by those skilled in the art;    -   doped or undoped Cs₂LiYBr₆ and particularly Cs₂LiYBr₆:Ce a        component usually called “CLYB” by those skilled in the art;    -   doped or undoped Cs₂LiYF₆ and particularly Cs₂LiYF₆:Ce, a        component usually called “CLYF” by those skilled in the art;    -   doped or undoped Cs_(2(1-z))Rb_(2z)LiTRX₆ and particularly        Cs_(2(1-z))Rb_(2z)LiTRX₆:Ce with z ranging from 0 to 1, TR        representing a rare earth;    -   doped or undoped Rb₂LiYX₆ and particularly Rb₂LiYX₆:Ce;    -   Cs_(2(1-z))Rb_(2z)LiTRI₆ with z ranging from 0 to 1, doped or        undoped and particularly Cs_(2(1-z))Rb_(2z)LiTRI₆:Ce, TR        representing a rare earth,    -   doped or undoped Cs₂LiY_((1-x))La_(x)Cl₆ and particularly        Cs₂LiY_((1-x))La_(x)Cl₆:Ce.

Thus, the scintillator material of structure of the elpasolite type oftheoretical composition A₂BC_((1-y))M_(y)X_((6-y)) and of real formulaA_(a)B_(b)C_(c)M_(m)X_(x) that can be fabricated by the processaccording to this disclosure can correspond to one of the cases below:

-   -   A is Cs, B is Li, C is a mixture of Y and Ce, and X is Cl;    -   A is Cs, B is Li, C is a mixture of La and Ce, and X is Br;    -   A is Cs, B is Li, C is a mixture of Y and Ce, and X is F;    -   A is Cs, B is Li, C is a mixture of La and Ce, and X is Cl;    -   A is a mixture of Cs and Rb, B is Li, C is a mixture of La and        Ce, and X is Br;    -   A is Cs, B is Li, C is a mixture of La and Ce, and X is a        mixture of Cl and Br;    -   A is Cs, B is Li, C is a mixture of Y and Ce, and X is a mixture        of Cl and Br.    -   A is Cs, B is Li, C is a mixture of La, Y and Ce, and X is Cl;    -   A is a mixture of Cs and Na, B is a mixture of Li and Na, C is a        mixture of Y and Ce, and X is Cl.

According to this disclosure, a substantial decrease or even thesuppression of the formation of unwanted phases is obtained by producingthe crystallization from a melt bath of composition offset with respectto the composition of the desired final crystal in the measure that itcontains a molar excess of B with respect to the theoreticalstoichiometry of the crystal. Moreover, the ratio of atomic fractions2b/a (of formula (2)) is closer to the theoretical stoichiometric ratioof 1, or even greater than 1.

The growth is initiated from a melt bath, the composition of which doesnot correspond exactly to the stoichiometric composition of theelpasolite, nor to the desired final composition of the elpasolite.Generally, the process according to this disclosure is of the“auto-flux” type, i.e. the melt bath contains no chemical element notfound at all in the crystal. If the liquid around or arriving around thecrystal is not of homogenous composition, what counts is that the excessof B (i.e. 2s/r>1) exists for the part of the liquid in direct contactwith the crystal. Indeed, the growth technique called “multi-crucible”according to which at least two crucibles are found nested one insidethe other can be used to perform the process according to thisdisclosure, as soon as the liquid composition in the innermost crucibleand in contact with the crystalline material satisfies the condition ofthe excess of B according to the invention.

The process according to this disclosure generally takes place in acrucible or a closed or even sealed phial. The crucible can particularlybe made of graphite with a pyrolytic coating, or of vitreous carbon. Theclosed or even sealed phial is generally made of quartz or vitreouscarbon or platinum.

According to this disclosure, the next step is to place the halogenatedraw materials into a container (crucible, phial, etc.) in anon-oxidizing atmosphere, then to heat it until the raw materials melt,then the crystalline growth is carried out according to the chosentechnique (Bridgman, Czochralski, etc.) and the container is cooled downto ambient temperature.

This disclosure can be conducted to result in a single crystal by usingone of the techniques known to those skilled in the art such as those ofCzochralski or Bridgman or Bagdasarov (horizontal Bridgman technique) orKyropoulos or else the “Vertical Gradient Freeze” technique(crystallization by control of the thermal gradient) or else so-calledEFG (Edge Feeding Growth) or the “continuous feeding” technique whichcovers the use of multi-crucibles, in particular the growth of crystalsin a double crucible, one of the crucibles nesting in the other.

The elpasolite single crystal can have a volume above 10 cm³ and evenabove 100 cm³. Even if the ingot of monocrystalline growth containsinclusions, the monocrystalline part free of inclusions can have avolume above 10 cm³ and even above 100 cm³.

Notably, the process according to this disclosure can lead to an ingotwhose first two-thirds in volume of growth of monocrystalline materialcomprise less than 10% in volume of any phase different to that of theelpasolite, which is noteworthy. In particular, in the case of aCzochralski monocrystalline growth process, the first two-thirds involume of growth of monocrystalline material cannot contain any phasedifferent to that of the elpasolite, which is also noteworthy.

It is also possible to prepare a polycrystal using the process accordingto this disclosure. To do this, it suffices to bring the mixture of rawmaterials to melting point and to cool the melted mass obtained withoutany particular precaution. Subsequently, it is possible to obtain thedesired sizes of granulate by crushing or milling. It is also possibleto obtain a crystalline powder by milling.

The raw materials used to produce the melt bath contain the elementsentering into the composition of the elpasolite. This can for exampleinvolve a mixture of a halide of A, a halide of B, a halide of C and ahalide of M. It then suffices to load an excess of B halide with respectto the intended stoichiometric composition for the final crystal. Forthe mixture of raw materials, this can also involve a mixture of severalhalides of which at least one comprises at least two of the elements A,B, C and M. Here again, it suffices to load an excess of the halidecontaining the element B, with respect to the intended stoichiometriccomposition.

Examples of components that can be used to form an excess of Liaccording to this disclosure are LiCl, Li₃Ycl₆, Cs₃Li₂Cl₅, Cs₂Li₃Cl₅,and Li₃LaBr₆.

The process according to this disclosure translates into a crystallinegrowth as a consequence of a controlled cooling of a bath of a meltedcomposition. This melted composition is obtained by melting onecomponent or a mixture of components as raw material (this component ormixture of components being called precursor) resulting in the desiredcomposition of the desired elements in the liquid bath. It is possibleto use a single component of a composition corresponding exactly to thatof the desired melt bath. It is also possible to use as raw material amixture of halides of various elements entering into the desiredcomposition. Thus, if one desires to fabricate a CLYC, it is possible tomix a chloride of Cs, a chloride of Li, a chloride of Y and, whereapplicable, a chloride of Ce (in the case of a Ce doping).

The excess of B according to this disclosure does not completely go intothe final crystalline material, and what does not go into it can berecovered as by-product after the solidification and notably re-used inthe context of the process according to the invention. If theCzochralski process of monocrystalline growth is used, the remainingexcess is found in the liquid phase remaining in the crucible. If theBridgman process of monocrystalline growth is used, the remaining excessis found in a region comprising inclusions, said region forming mainlyat the end of the process and being in any case of smaller proportionthan in the absence of excess.

The excess of B according to this disclosure can make it possible tobring the composition of the final crystalline material closer to theperfect stoichiometric composition A₂BC_((1-y))M_(y)X_((6-y)). When acrystallization is produced from a bath of a composition correspondingexactly to that of the intended elpasolite crystal, the stoichiometricdeficit is of the order of 2 to 3% in moles of B. To combat thisdeficit, this disclosure proposes to use an excess of B preferably of atleast 5% in moles (2s/r>1.05).

For a given elpasolite, there exists a minimum value of 2s/r at thelevel of the melt bath for which the first two-thirds in volume of ingotgrowth are entirely (100%) composed of said elpasolite. If t is thenumber of moles of C in the bath, then, the introduction into the bathof raw materials such that the 2t/r ratio above 1 and even above 1.08and even above 1.1, or even of at least 1.2, makes it possible to reducethe minimum value of 2s/r for which the first two-thirds in volume ofgrowth are entirely (100% in volume) composed of said elpasolite. Forone and the same volume of usable elpasolite in the first two-thirds ofthe fabricated ingot, the increase in the 2t/r ratio makes it possibleto reduce the 2s/r ratio. The increase in the 2t/r ratio can be producedby introducing into the melt bath components, particularly of the typeB₃CX₆ (B, C and X having the significance given previously) such asLi₃LaBr₆ or Li₃Ycl₆. This excess of C could also be produced by a largerquantity of CX₃. However, the use of components of B₃CX₆ type makes itpossible to produce an excess both of B and C. This effect of the high2t/r ratio on the ingot quality is particularly notable in the case ofelpasolites for which C is at over 80% in moles Lanthane and X is atover 80% in moles Bromine (elpasolith “rich in LaBr₃”). If the 2t/r ishigher, the perfect crystal yield is improved, particularly beyond thefirst two-thirds in volume of growth. In the case of a Bridgman growth,the quantity of unfit material is decreased at the end of growth (shadedpart of FIG. 1c particularly). In the case of a Czochralski growth, lessmaterial is left in the bath when the growth is ended. Increasing 2t/reven makes it possible to reduce 2s/r, for example to less than 1.65.

For the case of an elpasolite for which C comprises La, particularly ifC is at over 80% in moles Lanthane and for which X comprises Br,particularly if X is at over 80% in moles Bromine, particularly in thecase of an elpasolite of CLLB type, then the fact of having both 2t/rabove 1 and even above 1.08 and even above 1.1, or even at least 1.2,concomitantly with the fact of having 2s/r above 1.05, or even at least1.1 makes it possible to obtain a 2b/a of at least 1.1, or even of atleast 1.15 or even of at least 1.2, up to 1.4 particularly.

Rare earth halide elpasolites are generally hygroscopic and handled in asuitable atmosphere, i.e. dry and neutral or reductive (hydrogenatednitrogen, argon, nitrogen, hydrogenated argon) or in a vacuum. This alsoapplies to the measurement techniques used, which are to be performed ina suitable atmosphere, especially diffraction measurements. Diffractionmeasurements made in an unsuitable atmosphere (particularly ambient air)can falsify the measurements. The Bridgman process, which can make acrystallization occur in a vacuum-sealed phial (generally made of quartzor of vitreous carbon), is advantageous from this point of view, becausethe crystallization is easily achieved in a suitable atmosphere.

The temperature to which the melt bath is brought before crystallizationdepends on the formulation of the bath. In general, the bath is broughtto between 400 and 1100° C. according to composition, beforecrystallization. In the context of a monocrystalline growth process, thecooling speeds are generally between 0.01° C./hour and 5° C./hour. Inthe Bridgman process, the translation speed of the crystal generallylies between 0.01 mm/h and 20 mm/h. If a polycrystal of the elpasolitephase is sought, the cooling speeds can be much faster, notably lyingbetween 5 and 200° C./h.

FIG. 1 represents ingots taken out of their phial after crystallinegrowth of Bridgman type. Case a) corresponds to what is obtained in theprior art, i.e. a high volumetric level of unusable ingot because theingot comprises many inclusions (shaded parts), notably at the start ofthe growth, which corresponds to the lower part of the ingot. Thisnarrow part of the ingot is taken into account when expressing theresult and therefore counts as volume of growth according to theinvention. Case c) corresponds to the case according to the inventionwith a high level of usable single crystal. The shaded part at the topcorresponds to an undesired phase. The case b) corresponds to anintermediate situation with an excess of B below that used in c), whichhas led to a higher level of inclusions.

FIG. 2 represents ingots after crystalline growth of Czochralski type.The narrow part in the upper region corresponds to the monocrystallineseed used to initiate the growth. This part is not taken into accountwhen expressing the result. In a), the ingot is totally unusable becauseit is entirely polluted by inclusions and corresponds to the prior art,i.e. an absence of excess of B. In c), the ingot is perfect, devoid ofinclusions. An excess of B according to the invention has been used. Thecase b) corresponds to an intermediate case between cases a) and c),with an excess of B below that used in c).

Many different aspects and embodiments are possible. Some of thoseaspects and embodiments are described below. After reading thisspecification, skilled artisans will appreciate that those aspects andembodiments are only illustrative and do not limit the scope of thepresent invention. Embodiments may be in accordance with any one or moreof the embodiments as listed below.

Embodiment 1. A process for fabricating a crystalline scintillatormaterial with a structure of elpasolite type of theoretical compositionA₂BC_((1-y))M_(y)X_((6-y)) wherein

-   -   A is chosen from among Cs, Rb, K, Na,    -   B is chosen from among Li, K, Na,    -   C is chosen from among the rare earths, Al, Ga,    -   M is chosen from among the alkaline earths,    -   X is chosen from among F, Cl, Br, I,

y representing the atomic fraction of substitution of C by M and beingin the range extending from 0 to 0.05, comprising its crystallization bycooling from a melt bath comprising r moles of A and s moles of B,characterized in that the crystalline scintillator material is dopedwith an element activating its scintillation and in that the melt bathin contact with the material contains A and B in such a way that 2s/r isabove 1.

Embodiment 2. The process in the preceding embodiment, characterized inthat 2s/r is above 1.05.

Embodiment 3. The process in the preceding embodiment, characterized inthat 2s/r is above 1.15 and preferably above 1.25.

Embodiment 4. The process in the preceding embodiment, characterized inthat 2s/r is above 1.35 and preferably above 1.5.

Embodiment 5. The process in one of the preceding embodiments,characterized in that 2s/r is below 10 and preferably below 5 andpreferably below 3.

Embodiment 6. The process in one of the preceding embodiments,characterized in that 2s/r is enough for the ratio of the double of theatomic fraction of B-type element to the atomic fraction of the A-typeelement in the crystalline material to be of at least 0.97.

Embodiment 7. The process in one of the preceding embodiments,characterized in that M is chosen from among Ca, Mg, Sr or Ba.

Embodiment 8. The process in one of the preceding embodiments,characterized in that C comprises at least one activating rare earthchosen from among Ce, Pr, Eu, Tb and Nd, the atomic fraction of which issuch that the ratio of its atomic fraction to the sum of the atomicfractions of elements C and M in the crystalline material is above0.00001 and below or equal to 0.1.

Embodiment 9. The process in one of the preceding embodiments,characterized in that 2s/r is not enough to generate the formation of aphase of B₃C_((1-y))M_(y)X₆ at the start of the crystallization.

Embodiment 10. The process in one of the preceding embodiments,characterized in that B comprises Li.

Embodiment 11. The process in one of the preceding embodiments,characterized in that B is Li.

Embodiment 12. The process in one of the preceding embodiments,characterized in that X comprises Cl, Br or I.

Embodiment 13. The process in one of the preceding embodiments,characterized in that the rare earth comprises an element of theLanthanides from La to Lu, or Y.

Embodiment 14. The process in one of the preceding embodiments,characterized in that A comprises Cs and B comprises Li.

Embodiment 15. The process in the preceding embodiment, characterized inthat C comprises La and X comprises Br.

Embodiment 16. The process in one of the two preceding embodiments,characterized in that C is at over 80% in moles lanthanum and X is atover 80% in moles bromine.

Embodiment 17. The process in embodiment 14, characterized in that Ccomprises Y and X comprises Cl.

Embodiment 18. The process in the preceding embodiment, characterized inthat C is at over 80% in moles Y and in that X is at over 80% in molesCl.

Embodiment 19. The process in one of the preceding embodiments,characterized in that 2t/r is above 1, and even above 1.1 and even of atleast 1.2, t representing the number of moles of C in the bath.

Embodiment 20. The process in one of embodiments 1 to 15, characterizedin that 2t/r is above 1, and even above 1.1 and even of at least 1.2, trepresenting the number of moles of C in the bath, C comprises La,particularly with C at over 80% in moles La, and X comprises Brparticularly with X at over 80% in moles Br, and 2s/r is above 1.05, oreven at least 1.1.

Embodiment 21. The process in one of the preceding embodiments,characterized in that it is a monocrystalline growth process.

Embodiment 22. The process in the preceding embodiment, characterized inthat the first two-thirds in volume of growth of the monocrystallinematerial comprise less than 10% in volume of phase different to that ofthe elpasolite.

Embodiment 23. The process in the preceding embodiment, characterized inthat the crystallization is of Czochralski type in that the firsttwo-thirds in volume of growth of the monocrystalline material do notcontain any phase different to that of the elpasolite.

Embodiment 24. The process in one of the preceding embodiments,characterized in that the crystalline material is made from incongruentfusion.

Embodiment 25. A crystalline scintillator material doped with an elementthat activates its scintillation, of structure of elpasolite type oftheoretical composition A₂BC_((1-y))M_(y)X_((6-y)) and of real formulaA_(a)B_(b)C_(c)M_(m)X_(x) wherein

A is chosen from among Cs, Rb, K, Na,

B is chosen from among Li, K, Na,

C is chosen from among the rare earths, Al, Ga,

M is chosen from among the alkaline earths,

X is chosen from among F, Cl, Br, I,

y representing the atomic fraction of substitution of C by M and beingin the range extending from 0 to 0.05, a, b, c, m, and x representingthe respective atomic fractions of A, B, C, M, and X, the 2b/a ratiobeing in the range extending from 0.97 to 1.4.

Embodiment 26. The material in the preceding embodiment, characterizedin that C contains at least one activating rare earth chosen from amongCe, Pr, Eu, Tb, and Nd, the atomic fraction of which is such that theratio of its atomic fraction to the sum of the atomic fractions ofelements C and M is above 0.00001 and below or equal to 0.1.

Embodiment 27. The material in one of the preceding materialembodiments, characterized in that B comprises Li.

Embodiment 28. The material in the preceding embodiment, characterizedin that A comprises Cs.

Embodiment 29. The material in the preceding embodiment, characterizedin that C comprises La and X comprises Br.

Embodiment 30. The material in the preceding embodiment, characterizedin that C is at over 80% in moles lanthanum and X is at over 80% inmoles bromine.

Embodiment 31. The material in embodiment 27 or 28, characterized inthat C comprises Y and X comprises Cl.

Embodiment 32. The material in the preceding embodiment, characterizedin that C is at over 80% in moles Y and in that X is at over 80% inmoles Cl.

Embodiment 33. The material in one of the preceding materialembodiments, characterized in that X comprises Cl, Br or I.

Embodiment 34. The material in one of embodiments 25 to 28,characterized in that C comprises a rare earth chosen from among theLanthanides from La to Lu, or Y.

Embodiment 35. The material in one of embodiments 25 and 26,characterized in that A is Cs, B is Li, C is a mixture of Y and Ce, andX is Cl.

Embodiment 36. The material in one of embodiments 25 and 26,characterized in that A is Cs, B is Li, C is a mixture of La and Ce, andX is Br.

Embodiment 37. The material in one of embodiments 25 and 26,characterized in that A is Cs, B is Li, C is a mixture of La and Ce, andX is Cl.

Embodiment 38. The material in one of embodiments 25 and 26,characterized in that A is a mixture of Cs and Rb, B is Li, C is amixture of La and Ce, and X is Br.

Embodiment 39. The material in one of embodiments 25 and 26,characterized in that A is Cs, B is Li, C is a mixture of La and Ce, andX is a mixture of Cl and Br.

Embodiment 40. The material in one of embodiments 25 and 26,characterized in that A is Cs, B is Li, C is a mixture of Y and Ce, andX is a mixture of Cl and Br.

Embodiment 41. The material in one of embodiments 25 and 26,characterized in that A is Cs, B is Li, C is a mixture of La, Y and Ce,and X is Cl.

Embodiment 42. The material in one of embodiments 25 and 26,characterized in that A is a mixture of Cs and Na, B is a mixture of Liand Na, C is a mixture of Y and Ce and X is Cl.

Embodiment 43. The material in one of embodiments 25 and 26,characterized in that A is Cs, B is Li, C is a mixture of Y and Ce, andX is F.

Embodiment 44. The material in one of embodiments 29, 30 or 39,characterized in that the 2b/a ratio is in the range extending from 1.1to 1.4.

Embodiment 45. The material in one of embodiments 25 to 44,characterized in that the crystalline material is made from incongruentfusion.

Embodiment 46. The material in one of the preceding materialembodiments, characterized in that its scintillation energy resolutionis below 6%, or even below 5%, measured with a source of ¹³⁷Cs gammarays of 662 keV.

Embodiment 47. An ingot of monocrystalline growth comprising a materialof one of the preceding material embodiments, characterized in that thefirst two-thirds in volume of growth comprise less than 10% in volume ofphase different to that of the elpasolite material.

Embodiment 48. The ingot in the preceding embodiment, characterized inthat the first two-thirds in volume of growth of the monocrystallinematerial do not contain any phase different to that of the elpasolitematerial.

EXAMPLES

Powder mixtures are produced of raw materials of the type of halides ofthe cations to be inserted into the elpasolite.

Single crystals are produced by crystallization from melt baths, thecompositions of which are listed in table 1. The examples are accordingto this disclosure or are comparative and include in the latter case theannotation “comp”. The composition of the bath can be expressed globallyor by presenting it in the form of the sum of a stoichiometricelpasolite and the component or components put in excess, comprising B.In this table, BG means that a growth of Bridgman type has been used andCZ means that a growth of Czochralski type has been used. In the case ofexample 8, the sodium being able to go to the sites of the Cs or of theLi, it was noticed a posteriori that in the final crystal the proportionof Na on the Li sites was of 89% and the proportion of Na on the Cssites was of 11%. This is why, for 2 moles of Cs introduced into thebath, the quantity of A in the bath is of 2 (for the Cs)+0.074 (for 11%of 0.67 moles of Na) or 2.074 moles. The quantity of B in the bath is of1 (for the Li)+0.596 (for 89% of 0.67 moles of Na) or 1.596 moles. The2s/r ratio is therefore here of (2×1.596)/2.074=1.54.

In the case of a growth of the CZ type, not all the bath used istransformed into ingot material, in a manner inherent to this technique.On the contrary, in Bridgman crystallization, all the bath used hassolidified into the ingot. In the last column of table 1, the percentageof really usable single crystal in the first two-thirds of growth of thesolidified ingot is given. In CZ growth it is therefore not a questionof a percentage of the material used in the bath. On the other hand, inBridgman growth, it is also a question of a percentage of the materialused in the bath. Examples 20, 21, 22, 24 show that, in the case ofCLLB, a high 2s/r ratio in the bath leads to a 2b/a distinctly above 1in the elpasolite.

TABLE 1 % vol 2b/a usable Type of 2s/r 2t/r Final first ⅔ Ex no growthMelt bath composition bath bath Crystal composition obtained crystal ofingot  1 BG Cs₂Li₁Y_(0.995)Cl₆:Ce_(0.005) 1 1Cs_(2.035)Li_(0.982)Y_(0.982)Cl_(5.966):Ce_(0.001) 0.965 84 (comp)  2 BGCs₂Li₁Y₁Cl₆ 1 1 Cs_(2.046)Li_(0.972)Y_(0.982)Cl_(5.964) 0.95 82 (comp) 3 CZ Cs₂Li₁Y₁Cl₆ 1 1 — 0 (comp)  4 CZCs₂Li_(1.67)Y_(0.995)Cl_(6.67):Ce_(0.005) 1.67 1Cs_(1.997)Li_(0.998)Y_(1.004)Cl_(6.01):Ce_(0.001) 0.999 100 orCs₂Li₁Y_(0.995)Cl₆:Ce_(0.005) + 0.67 LiCl  5 BGCs₂Li_(1.249)Y_(1.078)Cl_(6.489):Ce_(0.005) 1.25 1.083Cs_(2.015)Li_(0.996)Y_(0.988)Cl_(5.978):Ce_(0.001) 0.989 100 orCs₂Li₁Y_(0.995)Cl₆:Ce_(0.005) + 0.083 Li₃Ycl₆  6 BGCs₂Li_(1.56)Y_(0.995)La_(0.1)Ce_(0.005)Cl_(6.86) 1.56 1.1Cs_(2.006)Li_(0.995)La_(0.008)Y_(0.989)Cl_(5.998):Ce_(0.002) 0.992 100or Cs₂Li₁Y_(0.995)Cl₆:Ce_(0.005) + 0.56 LiCl + 0.1 LaCl₃ 7 BGCs₂Li_(1.66)Y_(0.995)Cl_(6.66):Ce_(0.005) 1.66 1Cs_(2.005)Li_(0.995)Y_(0.999)Cl_(5.74):Ce_(0.001) 0.993 100 orCs₂Li₁Y_(0.995)Cl₆:Ce_(0.005) + 0.66 LiCl  8 BGCs₂Li₁Na_(0.67)Y_(0.995)Ce_(0.005)Cl_(6.67) 1.67 1Cs_(1.91)Li_(0.467)Na_(0.599)Y_(1.022)Cl_(6.048):Ce_(0.02) 1.012 100 oror Cs₂Li₁Ce_(0.005)Y_(0.995)Cl₆ + 0.67(Cs_(1.91)Na_(0.066))(Li_(0.467)Na_(0.533)) NaCl(Y_(1.022)Ce_(0.002))Cl_(6.048)  9 CZCs₂Li_(1.67)Y_(0.995)Ca_(0.003)Ce_(0.005)Cl_(6.676) 1.67 1Cs_(2.018)Li_(1.006)Ca_(0.001)Y_(0.974)Cl_(5.951):Ce_(0.001) 0.997 100or Cs₂LiY_(0.995)Ce_(0.005)Cl₆ + 0.67 LiCl + 0.003 CaCl₂ 10 BGCs₂Li_(1.67)Y_(0.995)Sr_(0.003)Ce_(0.005)Cl_(6.676) 1.67 1Cs_(2.005)Li_(1.071)Sr_(0.001)Y_(0.921)Cl_(5.847):Ce_(0.002) 1.068 100or Cs₂LiY_(0.995)Ce_(0.005)Cl₆ + 0.67 LiCl + 0.003 SrCl₂ 11 CZCs₂LiLa_(0.98)Ce_(0.02)Br₆ 1 1 — 0 (comp) 12 CZCs₂Li_(1.8)La_(0.99)Ce_(0.01)Br_(6.8) 1.8 1Cs_(2.009)Li_(1.01)La_(0.98)Br_(5.97):Ce_(0.001) 1.005 100 orCs₂Li₁La_(0.99)Ce_(0.01)Br₆ + 0.8 LiBr 13 BGCs₂Li₁Y_(0.995)Ce_(0.005)Br₆ 1 1Cs_(2.025)Li_(0.978)Y_(0.995)Br_(5.994):Ce_(0.002) 0.966 100 (comp) 14BG Cs₂Li_(1.1)Y_(0.995)Ce_(0.005)Br₆ 1.1 1Cs_(2.001)Li_(1.006)Y_(0.991)Br₆:Ce_(0.002) 1.005 100 orCs₂Li₁Y_(0.995)Ce_(0.005)Br₆ + 0.1 LiBr 15 BG Rb₂LiY_(0.99)Ce_(0.01)Br₆1 1 Rb_(2.027)Li_(0.976)Y_(0.996)Br_(5.994):Ce_(0.001) 0.963 76 (comp)16 BG Rb₂Li_(1.7)Y_(0.99)Ce_(0.01)Br_(6.7) 1.7 1Rb_(2.005)Li_(1.005)Y_(0.989)Br_(5.98):Ce_(0.001) 1.002 92 orRb₂LiY_(0.99)Ce_(0.01)Br₆ + 0.7 LiBr 17 BGCs₂Li_(1.60)Y_(0.9965)F_(6.6):Ce_(0.0035) 1.6 1Cs_(1.994)Li_(0.997)Y_(1.007)F_(6.018):Ce_(0.002) 1.017 100 orCs₂Li₁Y_(0.9965)F₆:Ce_(0.0035) + 0.6 LiF 18 CZCs₂Li_(1.6)La_(0.98)Ce_(0.02)Br₆Cl_(0.6) 1.6 1Cs_(1.961)Li_(1.051)La_(0.987)Br_(5.976)Cl_(0.051):Ce_(0.001) 1.072 100or Cs₂Li₁La_(0.98)Ce_(0.02)Br₆ + 0.6 LiCl 19 CZCs₂Li_(1.6)Y_(1.195)Cl_(7.2):Ce_(0.005) 1.6 1.2Cs₂Li_(1.001)Y_(0.998)Cl_(5.998):Ce_(0.001) 1.001 100 orCs₂Li₁Y_(0.995)Cl₆:Ce_(0.005) + 0.2 Li₃Ycl₆ 20 BGCs₂Li_(1.36)La_(1.118)Ce_(0.002)Br_(6.72) 1.36 1.12Cs_(1.884)Li_(1.113)La_(0.972)Ce_(0.031)Br_(6.006) 1.181 100 orCs₂Li₁La_(0.998)Ce_(0.002)Br₆ + 0.12 Li₃LaBr₆ 21 BGCs₂Li_(1.5)La_(1.13)Ce_(0.02)Br_(6.9)I_(0.05) 1.5 1.15Cs_(1.842)Li_(1.133)La_(0.996)Ce_(0.029)Br_(5.53)I_(0.52) 1.23 100 orCs₂Li₁La_(0.98)Ce_(0.02)Br₆ + 0.15 Li₃LaBr₆ + 0.05 LiI 22 BGCs₂Li_(1.5)La_(1.13)Ce_(0.02)Br_(6.95) 1.5 1.15Cs_(1.842)Li_(1.124)La_(1.004)Ce_(0.03)Br_(6.068) 1.22 100 orCs₂Li₁La_(0.98)Ce_(0.02)Br₆ + 0.15 Li₃LaBr₆ + 0.05 LiBr 24 BGCs₂Li_(1.5)La_(1.08)Ce_(0.02)Br_(6.8) 1.5 1.1Cs_(1.861)Li_(1.132)La_(0.976)Ce_(0.031)Br_(6.014) 1.22 100 orCs₂Li₁La_(0.98)Ce_(0.02)Br₆ + 0.1 Li₃LaBr₆ + 0.2 LiBr 25 BGCs₂Li_(1.55)Y_(1.098)Ce_(0.002)Cl_(6.85) 1.55 1.1Cs_(1.991)Li_(1.047)Y_(0.930)Ce_(0.032)Cl_(5.924) 1.05 100 orCs₂Li₁Y_(0.998)Ce_(0.002)Cl₆ + 0.1 Li₃Ycl₆ + 0.25 LiCl 26 BGCs₂Li_(1.453)Y_(1.148)Ce_(0.002)Sr_(0.003)Cl_(6.906) 1.45 1.15Cs_(1.98)Li_(1.026)Sr_(0.001)Y_(0.992)Ce_(0.001)Cl_(5.988) 1.04 100 orCs₂Li₁Y_(0.998)Ce_(0.002)Cl₆ + 0.15 Li₃Ycl₆ + 0.003 SrCl₂ 27 BGCs₂Li_(1.45)Y_(1.148)Ce_(0.002)Cl_(6.9) 1.45 1.15Cs_(1.944)Li_(1.054)Y_(1.001)Ce_(0.001)Cl_(6.004) 1.08 100 orCs₂Li₁Y_(0.998)Ce_(0.002)Cl₆ + 0.15 Li₃Ycl₆ 28 CZCs₂Li_(1.3)Y_(1.098)Ce_(0.002)Cl_(6.6) 1.3 1.1Cs_(2.041)Li₁Y_(0.958)Ce_(0.001)Cl_(5.918) 0.98 100 orCs₂Li₁Y_(0.998)Ce_(0.002)Cl₆ + 0.1 Li₃Ycl₆

Table 2 gives the scintillation properties of certain crystals alreadydescribed in table 1. It indicates the relative light output (column LOfor “light output”) measured with a gamma excitation of 662 keV, and theenergy resolution (full width at half-maximum of the scintillationpeak). The scintillation measurements were performed with a source ofgamma rays of ¹³⁷Cs type, a photomultiplier and a standard measurementsubsystem. The values obtained can be compared with each other becausethey are determined with a determined sample geometry and with the samemeasuring instruments. The lower the value of the energy resolution, thebetter it is. The light output is preferably as high as possible. Forcrystals of CLYC type, the light output has been expressed relative tothat of example 1 (LO evaluated at 1 arbitrarily). For crystals of CLLBtype, the light output has been expressed relative to that of example 11(LO evaluated at 1 arbitrarily).

TABLE 2 Relative LO Energy resolution CLYC ex 1 1 6.19% (reference) CLYCex 4 1.15 4.61% CLYC ex 5 1.28 5.15% CLYC ex 7 1.20 4.67% CLLB ex 11 18.73% (reference) CLLB ex 12 1.20 4.14%

FIGS. 1a ) and 1 c) represent phials after crystalline growth ofBridgman type according to the examples. Examples 1, 2 and 15 resultedin an ingot of the type of that in FIG. 1a ). Examples 5, 6, 7, 8, 10,13, 14 and 17 resulted in an ingot of the type of that in FIG. 1c ). Forthese examples 5, 6, 7, 8, 10, 13, 14, 17 the first two-thirds in volumeof the monocrystalline material growth comprise less than 10% in volumeof any phase different to that of the elpasolite. In these specificcases, the volume of impure phase is at 0%.

In the case of examples 15 and 16, it is shown that the first two-thirdsin volume of any phase different to the elpasolite phase can be loweredfrom 24% to 8% using the invention. Example 16 therefore results in aningot of the type in FIG. 1b ) or the first two-thirds in volume ofmonocrystalline material growth comprise less than 10% in volume of anyphase different to that of the elpasolite but more than 0%.

FIGS. 2a ) et 2 c) represent ingots after crystalline growth of theCzochralski type according to the examples. Examples 3 and 11 resultedin an ingot of the type of that in FIG. 2a ). Examples 4, 9, 12, 18 and19 resulted in an ingot of the type of that in FIG. 2c ). For theseexamples 4, 9 and 12, 18, and 19 the 100% in volume of growth of themonocrystalline material do not contain any phase different to that ofthe elpasolite.

It can indeed be seen that the examples according to this disclosureusing an excess of B (or 2s/r>1) give rise to far fewer inclusions andtherefore to a better single crystal fabrication yield. They also giverise to better scintillation performance.

In the case of examples 5, 6, 19, 20, 21, 22, 24, 25, 26, 27, and 28,the 2t/r in the bath was above 1 and the 2s/r in the bath was above1.08. In these cases, a corresponding growth was observed, according toits type, in FIG. 1c or 2 c, the perfect crystal yield being increased.In the case of a Bridgman growth, it is the shaded part of FIG. 1c thatwas reduced. In the case of a Czochralski growth, it is the quantity ofmaterial remaining in the bath that was reduced. In the case of examples7 and 27 the percentage of the mass of the unwanted phase at the end ofthe growth was measured (shaded part of FIG. 1c ) out of the total massof material introduced into the Bridgman phial. It was observed thatthis percentage is distinctly lower in the case of example 27 (10%) withrespect to that of example 7 (17.9%). The material yield is much higherin the case of example 27 compared to example 7.

Note that not all of the activities described above in the generaldescription or the examples are required, that a portion of a specificactivity may not be required, and that one or more further activitiesmay be performed in addition to those described. Still further, theorder in which activities are listed is not necessarily the order inwhich they are performed.

Benefits, other advantages, and solutions to problems have beendescribed above with regard to specific embodiments. However, thebenefits, advantages, solutions to problems, and any feature(s) that maycause any benefit, advantage, or solution to occur or become morepronounced are not to be construed as a critical, required, or essentialfeature of any or all the claims.

The specification and illustrations of the embodiments described hereinare intended to provide a general understanding of the structure of thevarious embodiments. The specification and illustrations are notintended to serve as an exhaustive and comprehensive description of allof the elements and features of apparatus and systems that use thestructures or methods described herein. Separate embodiments may also beprovided in combination in a single embodiment, and conversely, variousfeatures that are, for brevity, described in the context of a singleembodiment, may also be provided separately or in any subcombination.Further, reference to values stated in ranges includes each and everyvalue within that range. Many other embodiments may be apparent toskilled artisans only after reading this specification. Otherembodiments may be used and derived from the disclosure, such that astructural substitution, logical substitution, or another change may bemade without departing from the scope of the disclosure. Accordingly,the disclosure is to be regarded as illustrative rather thanrestrictive.

What is claimed is:
 1. A process for fabricating a crystallinescintillator material with a structure of elpasolite type of theoreticalcomposition A₂BC_((1-y))M_(y)X_((6-y)), comprising conductingcrystallization by cooling from a melt bath comprising r moles of A ands moles of B, wherein: A is chosen from among Cs, Rb, K, Na; B is chosenfrom among Li, K, Na and comprises Li; C is chosen from among the rareearths, Al, and Ga; M is chosen from among the alkaline earths; and X ischosen from among F, Cl, Br, and I and comprises Cl or Br or I, yrepresenting an atomic fraction of substitution of C by M and being in arange extending from 0 to 0.05; wherein the crystalline scintillatormaterial is doped with an element activating scintillation; wherein themelt bath in contact with the material contains A and B in such a waythat 2s/r is above 1; and wherein a first two-thirds in volume of growthof the crystalline material comprises less than 10% in volume of a phasedifferent to that of the elpasolite.
 2. The process as claimed in claim1, wherein 2s/r is above 1.05.
 3. The process as claimed in claim 1,wherein 2s/r is above 1.15.
 4. The process as claimed in claim 1,wherein 2s/r is above 1.25.
 5. The process as claimed in claim 1,wherein 2s/r is above 1.35.
 6. The process as claimed in claim 1,wherein 2s/r is above 1.5.
 7. The process as claimed in claim 1, wherein2s/r is below
 10. 8. The process as claimed in claim 1, wherein 2s/r isbelow
 5. 9. The process as claimed in claim 1, wherein 2s/r is below 3.10. The process as claimed in claim 1, wherein 2s/r is enough for aratio of a double of an atomic fraction of B-type element to an atomicfraction of the A-type element in the crystalline material to be of atleast 0.97.
 11. The process as claimed in claim 1, wherein M is chosenfrom among Ca, Mg, Sr, and Ba.
 12. The process as claimed in claim 1,wherein C comprises at least one activating rare earth chosen from amongCe, Pr, Eu, Tb and Nd, wherein a ratio of an atomic fraction of the atleast one activating rare earth to a sum of atomic fractions of elementsC and M in the crystalline material is above 0.00001 and below or equalto 0.1.
 13. The process as claimed in claim 1, wherein 2s/r is notenough to generate formation of a phase of B₃C_((1-y))M_(y)X₆ at startof the crystallization.
 14. The process as claimed in claim 1, wherein Bis Li.
 15. The process as claimed in claim 1, wherein the rare earthcomprises La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, orY.
 16. The process as claimed in claim 1, wherein A comprises Cs and Bcomprises Li.
 17. The process as claimed in claim 16, wherein Ccomprises La and X comprises Br.
 18. The process as claimed in claim 17,wherein C is at over 80% in moles lanthanum and X is at over 80% inmoles bromine.
 19. The process as claimed in claim 16, wherein Ccomprises Y and X comprises Cl.
 20. The process as claimed in claim 19,wherein C is at over 80% in moles Y and in that X is at over 80% inmoles Cl.
 21. The process as claimed in claim 1, wherein 2t/r is above1, t representing the number of moles of C in the bath.
 22. The processas claimed in claim 1, wherein: 2t/r is above 1, t representing thenumber of moles of C in the bath; C comprises La, wherein C is at over80% in moles La; X comprises Br, wherein X is at over 80% in moles Br;and 2s/r is above 1.05.
 23. The process as claimed in claim 1, whereinthe process is a monocrystalline growth process.
 24. The process asclaimed in claim 23, wherein the crystalline material is amonocrystalline material.
 25. The process as claimed in claim 24,wherein the process is a Czochralski type, wherein the first two-thirdsin volume of the growth of the monocrystalline material do not containany phase different to that of the elpasolite.
 26. The process asclaimed in claim 23, wherein the crystalline material is an ingot,wherein a first two-thirds in volume of the monocrystalline growthcomprises less than 10% in volume of a phase different to that of theelpasolite material.
 27. The process as claimed in claim 26, wherein thecrystalline material is a monocrystalline material, and the firsttwo-thirds in volume of the monocrystalline growth of themonocrystalline material do not contain any phase different to that ofthe elpasolite material.
 28. The process as claimed in claim 1, whereinthe crystalline material is made from incongruent fusion.
 29. Acrystalline scintillator material, wherein the crystalline scintillatormaterial: is doped with an element that activates scintillation; has astructure of an elpasolite type of a theoretical compositionA₂BC_((1-y))M_(y)X_((6-y)); and has a real formulaA_(a)B_(b)C_(c)M_(m)X_(x), wherein A is chosen from among Cs, Rb, K, Na;B is chosen from among Li, K, Na and comprises Li; C is chosen fromamong the rare earths, Al, Ga; M is chosen from among the alkalineearths; and X is chosen from among F, Cl, Br, I and comprises Cl or Bror I; y representing an atomic fraction of substitution of C by M andbeing in a range extending from 0 to 0.05, a, b, c, m, and xrepresenting respective atomic fractions of A, B, C, M, and X, a 2b/aratio being in a range extending from 0.97 to 1.4, wherein thecrystalline scintillator material is monocrystalline.
 30. Thecrystalline scintillator material as claimed in claim 29, wherein Ccontains at least one activating rare earth chosen from among Ce, Pr,Eu, Tb, and Nd, wherein a ratio of an atomic fraction of the at leastone activating rare earth to a sum of the atomic fractions of elements Cand M is above 0.00001 and below or equal to 0.1.
 31. The crystallinescintillator material as claimed in claim 29, characterized in that Acomprises Cs.
 32. The crystalline scintillator material as claimed inclaim 31, wherein C comprises La and X comprises Br.
 33. The crystallinescintillator material as claimed in claim 32, wherein C is at over 80%in moles lanthanum and X is at over 80% in moles bromine.
 34. Thecrystalline scintillator material as claimed in claim 32, wherein the2b/a ratio is in the range extending from 1.1to 1.4.
 35. The crystallinescintillator material as claimed in claim 31, wherein C comprises Y andX comprises Cl.
 36. The crystalline scintillator material as claimed inclaim 35, wherein C is at over 80% in moles Y and X is at over 80% inmoles Cl.
 37. The crystalline scintillator material as claimed in claim29, wherein; A comprises Cs; C comprises La and Ce; and X comprises Br.38. The crystalline scintillator material as claimed claim 29, wherein Ccomprises La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, orY.
 39. The crystalline scintillator material as claimed in claim 29,wherein A is Cs, B is Li, C is a mixture of Y and Ce, and X is Cl. 40.The crystalline scintillator material as claimed in claim 29, wherein Ais Cs, B is Li, C is a mixture of La and Ce, and X is Br.
 41. Thecrystalline scintillator material as claimed in claim 29, wherein A isCs, B is Li, C is a mixture of La and Ce, and X is Cl.
 42. Thecrystalline scintillator material as claimed in claim 29, wherein A is amixture of Cs and Rb, B is Li, C is a mixture of La and Ce, and X is Br.43. The crystalline scintillator material as claimed in claim 29,wherein A is Cs, B is Li, C is a mixture of La and Ce, and X is amixture of Cl and Br.
 44. The crystalline scintillator material asclaimed in claim 29, wherein A is Cs, B is Li, C is a mixture of Y andCe, and X is a mixture of Cl and Br.
 45. The crystalline scintillatormaterial as claimed in claim 29, wherein A is Cs, B is Li, C is amixture of La, Y and Ce, and X is Cl.
 46. The crystalline scintillatormaterial as claimed in claim 29, wherein A is a mixture of Cs and Na, Bis a mixture of Li and Na, C is a mixture of Y and Ce, and X is Cl. 47.The crystalline scintillator material as claimed in claim 29, wherein Ais Cs, B is Li, C is a mixture of Y and Ce, and X is F.
 48. Thecrystalline scintillator material as claimed in claim 29, wherein thecrystalline material is made from incongruent fusion.
 49. An ingotcomprising a crystalline scintillator material of claims 48, wherein afirst two-thirds in volume of a monocrystalline growth of the ingotcomprises less than 10% in volume of a phase different to that of theelpasolite material.
 50. The ingot of claim 49, wherein the firsttwo-thirds in volume of the monocrystalline growth does not contain anyphase different to that of the elpasolite material.
 51. The crystallinescintillator material as claimed in claim 29, wherein the crystallinescintillator material has a scintillation energy resolution below 6%,measured with a source of ¹³⁷Cs gamma rays of 662 keV.
 52. An ingotcomprising a crystalline scintillator material of claim
 29. 53. Amonocrystalline scintillator material, wherein the monocrystallinescintillator material is doped with an element that activatesscintillation; has a structure of an elpasolite type of a theoreticalcomposition A₂BC_((1-y))M_(y)X_((6-y)); and has a real formulaA_(a)B_(b)C_(c)M_(m)X_(x), wherein A comprises Cs; B comprises Li; C ischosen from among the rare earths, Al, Ga; M is chosen from among thealkaline earths; and X comprises Cl or Br; y representing an atomicfraction of substitution of C by M and being in a range extending from 0to 0.05, a, b, c, m, and x representing respective atomic fractions ofA, B, C, M, and X, a 2b/a ratio being in a range extending from 0.97 to1.4.
 54. The monocrystalline scintillator material of claim 53, whereinC comprises La and X comprises Br.
 55. The monocrystalline scintillatormaterial of claim 53, wherein C comprises Y and X comprises Cl.